ALTERATIONS IN PENICILLIN-BINDING PROTEINS IN STRAINS OF STREPTOCOCCUS-SUIS POSSESSING MODERATE AND HIGH-LEVELS OF RESISTANCE TO PENICILLIN

We examined the penicillin-binding proteins (PBPs) of certain field st rains of Streptococcus suis, as well as those from laboratory variants having different degrees of resistance to penicillin. Results indicat ed that (i) S. suis possesses three distinct groups of PBPs, arbitrari ly named here PBP 1, PBP 2, and PBP 3, with approximate molecular weig hts of 97, 82, and 45 kDa respectively; (ii) PBP profiles of field str ains of S. sds having different MICs ( less than or equal to 0.03 to 1 6.0 mu g/ml) were not uniform (PBP 2 being difficult to detect in stra ins whose MICs exceeded 0.10 mu g/ml, and PBP 3 which exhibited shifts in molecular weight of approximately 5 kDa); (iii) laboratory variant PBPs 1 and 2 showed decreased affinity for penicillin as compared to the parent strain in antibiotic competition experiments, even though t he PBP profiles of both were similar. We suggest that PBP modification s (altered molecular weight and/or decreased affinity for penicillin) are involved in the mechanism of resistance to penicillin by S. suis.